I sent Mat from Techmoan one of my latest design Mi Esposita nixie watchs as I thought he was the perfect person to do a review of it. Some of you may have seen the video already, but for the ones who haven't, here it is. The choice to go for a single tube watch was for two main reasons. First of all, it allowed me to make the world's smallest nixie watch but second (and most important) it would save a lot of battery power. A 2 tube watch would consume twice the amount of battery current. In a solar powered watch, you want to use as little power as possible so the choice for a single tube was obvious. Another reason is that it gives me the brightest digits for a given battery current. At maximum brightness (200mA battery current), a 4mA current runs through 1 digit, that is extremely bright. The Kopriso Cold War nixie watch with 2 tubes has a maximum current of 2mA per tube and "the other available" nixie watch only has 1mA current per tube. So 4mA really is very bright which is great for reading the time when you're outside. Another reason is tube failure. Some nixie tubes fail, usually shorting out a cathode to an anode. It doesn't happen very often but still, the chance is reduced by 50% in a single tube watch so that saves me in potential warranty repairs.

The tubes are at maximum brightness in a 2,000lux ambient light environment (the cold war in a 1,000lux environment). The continuous current drawn by the controller to keep time is 2.2uA and the total current for motion sensor, battery charge and protection circuit is about 1uA. The solar current from the panels breaks even with these continuously drawn currents at around 100lux. So any light above 100lux will contribute to charging the battery. In reality though, you need around 8 minutes of direct sunlight (100,000 lux) for each day the watch is used; which is based on 30 time readings in that day. A fully charged battery should last for about 1 year with 30 average indoor readings per day (11,000 readings per battery charge).